The present invention relates to a method and apparatus for optically inspecting magnetic media (magnetic dicks).
An aluminum (Al) substrate or a glass substrate is used as a substrate for a magnetic disk. As for the glass substrate, crystallized glass (SX) or amorphous glass (MEL) is used according to the application. Further, in each of the types of glass, a plurality of types of glass containing different components are used.
There is a possibility that small concave (pit) defects and small convex (bit) defects may occur on the surface of the glass substrate during the production process. The glass substrate having such small defects is likely to be defined as a defective product in the final inspection process. Thus, it is desirable that such a glass substrate likely to be defined as a defective product should be removed from the line in the initial process of the production line for the purpose of maintaining high production yield.
As for the conventional apparatus for inspecting defect on the surface of a magnetic disk, for example, Japanese Patent Application Laid-Open Publication No. 2000-180376 describes a method of irradiating a magnetic disk as a sample to be inspected with a laser beam, receiving the reflected light and scattered light from the surface of the magnetic disk by a plurality of detectors, and classifying small defects according to the light receiving conditions in each optical receiver. Further, the method also determines the plane continuity of the detected small defects to classify the magnitude of the length of the defects and classify as linear defects and block defects.
Further, Japanese Patent Application Laid-Open Publication No. HEI 10(1998)-253543 discloses a method of irradiating the inspection surface of a substrate to be inspected with a parallel light at the right angle, imaging the reflected light from the inspection surface, detecting concave or convex defects on the inspection surface as part of irregular brightness, converting the number of detected defect pixels of the detected defect into thirty error count values MCF corresponding to the number of missing errors when the substrate is integrated into media, and ranking the quality of the substrate based on the corresponding value MCF.